Thermostatic switch and method of assembly



Oct. 19, 1965 R. J. RUCKRIEGEL ETAL 3,212,351

THERMOSTATIC SWITCH AND METHOD OF ASSEMBLY Original Filed May 29, 1961 4 Sheets-Sheet 1 6 12 7' r 13 I1 Li I l I 39 7 1 2 1 (1 2 3 H gW/x// A /AM! I J EJI 'J' i Z L' I 33 K 29 I 1 l 27 25 g 1 5, 5/ 3 I F FIG 2 49 II 53 I 55 5 652; 5 i A 15 Oct. 19, 1965 R. J. RUCKRIEGEL ETAL 3,212,351

THERMOSTATIC SWITCH AND METHOD OF ASSEMBLY Original Filed May 29, 1961 4 Sheets-Sheet 2 Oct. 19, 1965 J RUCKRIEGEL L 3,212,351

THERMOSTATIC SWITCH AND METHOD OF ASSEMBLY Original Filed May 29, 1961 4 Sheets-Sheet 3 FIG. 7 51 Oct. 19, 1965 R. J. RUCKRIEGEL ETAL 3,212,351

STATIC SWITCH AND METHOD OF ASSEMBLY Original Filed May 29. 1961 4 Sheets-Sheet 4 6 I T 5Q 55 65 3 :2: a f f 7 59 7/ 7 59 7 l 8/ -73 35 I I I r" I I 7 1 1 f FIG. I 2/ 3-15 United States Patent 3,212,351 THERMOSTATIC SWITCH AND METHDD 0F ASSEMBLY Raymond Joseph Ruckriegel and Frederick A. Kirchhuhel, Versailles, and John 0. Moorhead, Lexington, Ky, assignors to Texas Instruments Incorporated, Dallas,

Tex., a corporation of Delaware Original application May 29, 1961, Ser. No. 113,502, now Patent No. 3,164,702, dated Jan. 5, 1965. Divided and this application Aug. 17, 1964, Ser. No. 389,990

2 Claims. '(Cl. 74-503) This invention relates to thermostatic electrical switches, and with regard to certain more specific features, to switch structure adaptable for assembly of both the automatic and manual reset type switches of this class.

This application is a division of our copending application Sernial No. 113,502, filed May 29, 1961, eventuated as Patent 3,164,702, for Thermostatic Switch and Method of Assembly.

Among the several objects of the invention may be noted the provision of thermostatically controlled electrical switches and particularly the snap-acting type, incorporating improved features of form and adjustment adapted to save manufacturing costs while preserving the accurate dimensional relationships required for a high-quality product; and the provision of switches of the class described which may conveniently be made up in both so-called automatic reset and manual reset types. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts which will be exemplified in the constructions and methods hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is an axial section of a primary subassembly of parts useful for constructing either an automatic or manual reset type of thermostatic switch;

FIG. 2 is a view similar to FIG. 1, showing the addition of certain parts to produce an automatic reset type of switch from the parts shown in FIG. 1;

FIG. 3 is an axial section of a manual reset button assembly adapted for the construction of a manual reset form of the switch;

FIG. 4 is a view similar to FIG. 3, showing a preliminary assembly step employed for producing the assembly of FIG. 3;

FIG. 5 is a cross section taken on line 5-5 of FIG. 3 and showing the manual reset button assembly applied to produce a manual reset type of switch;

FIG. 6 is a subassembly of switch parts, and of the manual reset button subassembly illustrated in FIGS. 3-5, showing a preliminary adjustment step employed for producing a manual reset form of the switch;

FIG. 7 is a cross section of a completed manual reset switch after adjustment, the switch being shown in closed position; and

FIG. 8 is a view similar to FIG. 7, showing the manual reset type of switch in open-circuit position.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

The manufacture of thermostatic switches employing transfer pins or the like has heretofore been beset with certain difficulties among which with regard to both the automatic and manual reset types are the following. If a pin is too short it may not transfer sufficient motion to open the contacts properly upon tripping. If it is too long, it may transmit undesirable creep action of the thermostat to the contacts, or the switch may not close. In the manual reset type an excessively long pin will permit the operator to hold the contacts closed while the temperature rises to an unsafe condition. In most applications this is undesirable, and in many it is mandatory that it shall not be possible. Since in many thermostats the usable working travel of the thermostatic disc used as a sensing element is small, a total travel of .010" being not uncommon, the selection of the proper reset pin length becomes bothersome and expensive.

Briefly, the switch made according to the present invention comprises a primary subassembly, with contacts therein operated by a snap-acting thermostatic disc which delivers its motion to one of the contacts through a transfer pin or the like. In one form of the switch, the snapacting disc may be of the automatic reset type, so that no manual reset mechanism is required. In another form of the switch, the snap-acting disc may be of the manual reset type, requiring a manual reset mechanism. By means of the invention, certain adjustments are provided during assembly which will permit the use of fairly widely variable lengths of transfer pins without encountering the stated difiiculties. This is accomplished by providing adjustments that can be made during assembly to accommodate dimensional variations in parts of the assembly. Selection of parts of exactly correct sizes is no longer required, and the individual parts do not require individual measurements, sorting or stocking, preparatory to assembly. They need to be only of approximately correct sizes. Of advantage is the fact that a subassembly such as shown in FIG. 1 may be used either for production of automatic reset or manual reset switches. In addition, a low-cost, four-part reset preassembly such as shown in FIGS. 3 and 4 is employed for making manual reset switches, which may be assembled and stocked for use as required. The four parts constituting this reset assembly require no gaging during their initial assembly with one another as a unit and may therefare be brought together in a minimum of time as a subassembly to be stocked for final assembly, provision being made for final adjustment at that time.

Referring now more particularly to FIG. 1, which shows a primary subassembly, there is illustrated a body structure 1 in the form of a housing or frame composed of molded insulating material. The body 1 is made up with a cup-shaped cylindrical portion 3, having an outside flat shoulder 5 which establishes a reference plane AA. Extending from the top of the body 1 is a flange formation 7. The top of the body 1 is slotted through the formation 7 to an appropriate depth for the reception of conductive terminal strips 9 and 11. The strips 9 and 11 are held by rivets 13 in openings 15 of the body 1. A nest 2 is formed by the flange formation 7. The shape of the nest 2 appears best in FIG. 5, wherein an alternative part to be described is nested. In FIG. 2 the nest 2 is shown as being for the reception of a flat cover 17 formed of electrically insulated material. This is the case when the subassembly of FIG. 1 is to be employed for the production of an automatically resettable device such as shown in FIG. 2.

At numeral 19 is shown a central axial opening (preferably cylindrical in cross section) for the reception of a ceramic or like insulating transfer pin 21 of like cross section. Such pins are not readily obtainable to close tolerances in length. At numeral 23' is shown an outside-access opening, the inner end of which is threaded for the final reception of a set screw 25.

The terminal strip 9 is riveted in place either before the set screw is inserted or, if the set screw is inserted, before it has been advanced. Terminal strip 9 is origiable and thus constitute adjustable hinge means.

nally so formed that when it is initially riveted in place its inner end assumes the dotted-line position shown at the upper left in FIG. 1, with the screw either missing or backed olf if inserted. This inner end 10 carries a fixed contact 27. Attached to the inner end 12 of terminal 11 is a cantilever spring contact arm which carries a movable contact 31. This spring arm extends transversely across the end of pin 21. The inner ends 10 and 12 of terminals 9 and 11, respectively, are bend- In its initially riveted position.(either before the'set screw is inserted or, if it is inserted, backed off) the terminal 9 is formed at angle C, as shown by the dotted lines in FIG. 1.

Next, a transfer pin 21, which may be a master or one from a lot to be used, is inserted into the opening 19 and located with its lower end at the distance D from plane AA (for example, at .070 inch). This distance has been predetermined as the one to be downwardly terminated by end 37 of pin 21 within the pure snapacting range of bimetallic thermostatic disc 47 such as shown in FIG. 2. The pin is held in this position by means of a suitable fixture which is capable of holding the pin 21 at distance D against downward force on the pin up to a certain critical value, say three ounces. The fixture is provided with means indicating when such critical force has been reached. There are various jigs and fixtures available for the purpose. The critical force is that which determines the contact pressure of several ounces between contacts, to, be described.

Next, with the pin 21 positioned as above described,

the inner end of the terminal 11 is bent from its original dotted-line position 6 to cause the spring arm 29 to engage the top of the pin. Bending is continued until said pressure, for example, three ounces, is indicated by the fixture at distance D. It will be appreciated that, after bending has been completed, with the pin in the location stated, which is its solid-line position in FIG. 1, the inner end 10 of the terminal strip 9 is still in its dotted-line position at angle C with the contacts open. Then set screw 25 may be inserted (or if already inserted in its backed-oft position) may be screwed in until the fixed contact at the inner end of strip 9 just touches the movable contact 31 in the solid-line position shown in FIG. 1. At this time, pin 21 is held in place as indicated in FIG. 1. This bends the inner end 10 of terminal 9 upward, so as to reduce the angle C. This finally bent position is maintained by the set screw 25 in its final position. It will be understood that while the screw 25 is a convenient means for etfecting this bending operation, it might be omitted and the bending of the inner end 10 of strip 9 accomplished otherwise. The subassembly of FIG. 1 is now in a condition that when the fixture is removed, whether or not the pin is left in place, the assembly will have the proper contact pressure for subsequent operation of the switch.

As will be noted from FIGS. 1 and 2, the spring arm 29 carries on its underside a lug 33 and on its upper side a lug 35. Use of these will be described below.

The completed structure for constructing an automatic reset switch is shown in FIG. 2. The cover 17 is held by fasteners, one of which is shown at 39. The other end of the body 1 is covered by a telescoped metal cup 41 which is held in position by dimples 49 formed in grooves 51. The cup 41 is flanged to form ears 42 in which are openings 44 for supporting or mounting purposes. The cup 41 is also formed with a shoulder 43, which is forced up against shoulder 5 so as accurately to position a shelf portion 45 thereof. Resting upon the shelf portion 45 is a bimetallic snap-acting thermostatic disc 47, the normal contacts-closed position of which is downwardly convex as shown, and the snapped contactsopen or tripped position of which is upwardly convex. It will be understood that the established distance D (FIG. 1) takes into account the curvature of the disc 47,

so that after assembly as shown in FIG. 2, a clearance K is established between the upper end of the transfer pin and the lower lug 33 when the pin 21 rests on the disc 47. This clearance, by allowing some free movement of the pin 21 between lug 33 and disc 47, permits initial inherent slow creep of the disc from its extreme contacts-closed configuration to an intermediate critical snap-acting configuration at which it snaps upward to its other extreme contacts-open configuration. Thus this clearance K assures that the preliminary creep action of the disc is not translated into preliminary creep opening of the contacts 27 and 31. As a result, these contacts are opened only in response to snap movement of the disc. This minimizes arcing at the contacts. The gaged adjusting means above described assures an accurate economical correlation of controlling factors, where these are of a low order of magnitude and were heretofore diflicult and costly to control. This was particularly true in view of the fact that small ceramic pins such as 21 are not obtainable in closely matched lengths. In practice, such pins may be very small, such as on the order of A3 inch in diameter and inch long, and their forming methods do not result in close tolerances. But, despite this, according to the present invention, close operating tolerances are obtained at low cost.

The subassembly of FIG. 1 is intended not only for the automatic reset switch of FIG. 2 but also for use in manufacturing manual reset switches, such as illustrated in FIGS. 5, 7 and 8. For such manual reset switches, manual reset buttons are required. For that purpose a manual reset button subassembly such as shown in FIGS. 3 and 4 is employed. This will be described before describing the manual reset switch as a whole and its complete method of manufacture, part of which involves what was described in connection with FIG. 1.

Referring to FIGS. 3 and 4, there is shown at numeral 53 a four-piece capping assembly which has an upwardly extending sleeve 55. Sleeve 55 which forms a guide is provided with an inner stop-forming flange 56 and a lower outer flange 57. From flange 57 extend transverse ears 59. The assembly 53 is designed to replace the cover 17 shown in FIG. 2. The replacement 53 is illustrated in FIG. 5 and, as will be seen from that figure, the cap is nested in the flange 7, instead of the flat cover 17 as in FIG. 2. Hold-down screws are shown at 61.

The sleeve 55 is provided with an internal upper shoulder-forming counterbore 63. The inner flange 56 is provided with two opposite axial slots 65. Beneath the slots 65 is a second counterbore 67. Openings 69 connect the counterbore 67 with the tops of the ears 59. At numeral 71 is shown a leaf spring in which is a central opening 73. Upwardly projecting fingers 75 are struck up from spring 71 on opposite sides of opening 73. Spring 71 is easily slipped into position by pushing it through one opening 69 and resting its ends in these openings 69. It and its fingers 75 are flexible enough for this purpose.

At 77 is shown a reset pin, the lower end of which is shouldered as shown at 79 for resting on the spring 71 and for providing a boss 81 extending into the opening 73 in the spring 71.- Extending oppositely from the shoulder portions 79 are bayonet-type lugs 83 adapted to pass through the slots 65. Attached to the upper end of the pin 77 by means of a medium force fit is a buttonforming split sleeve 85.

The reset pin 77, with the split ring 85 attached thereto, is dropped down into the sleeve 55 in a position wherein the lugs 83 slide down the slots 65. The lugs 83 can then be pushed down on the fingers 75, thereby bowing the spring 71 downward, allowing the lugs to emerge downwardly from the slots 65 (FIG. 4). They may then be turned at right angles from the position shown in FIG. 4 to that shown in FIG. 3. This positions the lugs 83 between the fingers 75, which then spring into the FIG. 3 position. Since the lugs 83 are now disaligned from the slots 65, the reset pin 77 cannot escape upward. Then, because of fingers 75 interfering with return rotation of the lugs 83, the reset pin 77 cannot be turned sufiiciently to bring the lugs 83 into alignment with the slots 65. The only substantial reset pin movement then possible is its limited axial movement, the amount of which is limited by engagement of the ring 85 with the shoulder 56. Reset button subassemblies such as illustrated in FIG. 3 may be carried in stock, ready for application to primary subassemblies such as shown in FIG. 1, for the production as desired of manual reset switches such as illustrated in FIGS. 58.

Although the button-forming ring 85 is shown as being slit, it may be a solid ring, providing an appropriate force fit of a nature permitting the desired adjustment described. In addition, it may have an internally splined or like connection with the reset pin 77. The primary requirement is that the interference fit shall be capable of holding the adjusted effective length of the reset pin throughout the useful life of the switch under normal environmental conditions of temperature, humidity, vibration and reset cycling, while at the same time allowing for the original press-fit adjustment by tool 87 (FIG. 6).

In FIG. 6 is illustrated how each stocked manual reset button subassembly (FIGS. 3 and 4) is applied and adjusted upon assembly for making a manual reset type of switch, which employs a manual reset type disc. After adjustment as above described in connection with FIG. 1 to obtain dimension D, further adjustments are made as follows: Downward pressure is exerted by the adjusting tool 87 upon the reset pin 77. This at first also moves down the ring 85 until it engages the shoulder 56. Upon continued application of force (say 70 lbs. or so) from the adjusting tool 87, the force of the fit between the ring 85 and the reset pin 77 is overcome. Movement is continued to drive down the pin 77 which, through lugs 35 and 33, drives down the pin 21 which by suitable means may be held against lug 33 holding contact 31 a definite distance away from contact 27. Adjustment is continued until dimension Y is obtained between plane A-A and the lower end of the pin 21. This dimension has been predetermined to bring about the functions which are discussed below. Upon removal of the tool 87, reset pin 77 will move upward, as shown in FIG. 7, by a distance T under the raising action of spring 71. This introduces a clearance K between the underside of boss 81 and upper lug 35. This is in addition to the clearance K which occurs between lower lug 33 and the upper end of pin 21. The distance Y is that which has been predetermined to give this proper clearance K. It will be recalled that the clearance K has already been obtained through the adjustments accomplished as described in connection with FIGS. 1 and 2.

The disc 89 is located in a cup 41. The cup is the same as that already described in connection with the automatic reset switch shown in FIG. 2. The assembled manual reset switch, ready for operation, is shown in the contacts-closed position of its manual reset disc 89 in FIG. 7. It will be seen that in FIG. 7 there are two clearances, namely, the lower clearance K like the clearance K in FIG. '2, and the clearance K. The clearance K is between the lower lug 33 and the upper end of the transfer pin 21 which, as before, prevents the initial operating creep movement of the thermostat 89 from its contactsclosed position toward its critical configuration from transmitting slow actuating movement to the contact 31. The only opening movement transmitted to contact 31 is that which occurs upon snap action provided by the disc 39 after it has passed through its creep movement. The clearance K at this time permits the upward rapid movement of contact 31 (compare FIGS. 7 and 8).

Upon pushing down the button-forming ring 85, in order manually to reclose the switch, its motion is limited by engagement of its lower margin with the shoulder 56. This motion is sufiicient to push the transfer pin 21 (via lugs 35 and 33) to bow down the disc 89 sufl'iciently to reach its critical configuration beyond which it will snap back to the position shown in FIG. 7, if cool enough. However, the available travel T of the reset pin is insufficient to drive the disc all the way to its extreme cold downwardly convex position. Thus the pin 21 cannot be manually driven down far enough to close the contacts 27 and 31, should the disc 89 not be cool enough to cause it spontaneously to assume its downwardly dished position. In other words, the movement of the reset pin is only suflicient to how a hot disc to but not through its critical condition for snap action, which latter will not occur unless the disc is cooled sufficiently. Under hot conditions, the contacts 27 and 31 remain open. It will therefore be evident that, by means of the adjustments above described the mannual reset type of form of the switch shown in FIGS. 7 and 8 is trip-free.

In view of the above, it will be seen that the mechanical actuation of the switch contacts 27 and 31 occurs only within the so-called pure snap range of the bimetallic disc, whether the switch incorporates an automatic reset type or a manual reset type of thermostatic disc. Stated otherwise, movement of the disc in its creep range prior to pure snap movement is not permitted to be transmitted to the contacts during any action. And in addition the switch is trip free. Ordinarily these features would be difticult to accomplish because of the former requirements for stocking many sizes of presorted carefully gaged parts and the need for selective assembly of the same. As a result of the invention, switches of improved controlled quality and lower cost may be made.

It should be understood that although the invention has been described to open the contacts upon temperature rise, it is equally applicable on an automatic reset type of switch wherein the contacts close upon temperature use In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A unitary control assembly for trip-free use on manual reset thermostatic electrical switches comprismg:

a housing having means for attachment to such a switch,

a guide sleeve having outer and inner end portions and extending from said attachment means,

said guide sleeve having at least one inside axial slot,

a switch-operating reset pin extending through said sleeve,

one end of said reset pin having an axially directed switch-operating means and at least one tansverse lug for passage through said slot when the pin is inserted through said sleeve,

a transversely directed return spring extending across the inner end portion of the sleeve and engaged by said switch-operating means,

at least one ear on the spring extending toward the inner end of said slot for engagement by said lug upon insertion of the pin through the sleeve thereby substantially to deflect the spring to admit the lug for location under the sleeve,

said ear upon rotation of the pin preventing realignment of the lug with the slot when the spring returns after said substantial deflection,

said spring being arranged to push back the pin until the lug engages the inner end portion of said sleeve when the lug is unaligned with the slot, whereby the pin is held against separation from the sleeve and 7 said switch-operating means is located to accommodate switch-opening action of the thermostatic switch,

a manual control member adjustably connected to the outer end of the reset pin for engagement with the outer, end portion of said sleeve, the adjusted position of the control member on the pin being such as to limit pin movement by said engagement to provide for trip-free switch operation by said control member of the thermostatic switch.

2. A unitary push-button control assembly for attachment to and trip-free control of manual reset thermostatic electrical switches comprising:

a housing having an outer portion for attachment to a switch,

a guide sleeve extending from said outer portion,

said guide sleeve having an inside flange portion formed by an outer counterbore and by an inner counterbore, the latter being adjacent said outer portion,

a return spring of leaf form extending across the inner counterbore, said outer portion having openings for supporting end portions of said spring after reception thereof by flexing it,

said inside flange portion having axial slots connecting the counterbores,

a reset pin in the guide sleeve and extending through said inisde flange portion,

one end of said reset pin having an axially directed switch-operating boss and transverse lugs for entry into the inner counterbore through said slots respectively upon insertion of the pin through said inside flange portion,

ears on the spring extending toward said inside flange portion at said slots respectively for engagement by said lugs upon insertion of the pin through the inside flange portion substantially to deflect the supported spring and upon rotation of the pin to prevent realignment of the lugs with the slots when the supported spring returns after substantial deflection, whereby the pin is pushed back until the lugs engage said inside flange portion.

said spring having an opening between its supports for reception of said boss,

a control push button adjustably connected to the outer end of the pin for location in the outer counterbore,

whereby the button may be located on the pin at a distance from said inside flange portion acting as a stop to provide limited pin movement for trip-free thermostatic switch operation.

References Cited by the Examiner UNITED STATES PATENTS 1,695,496 12/28 Jacques. 2,545,988 3/51 Bobrick 74-502 2,753,421 7/56 Mertler 200138.3 2,813,171 11/57 Cardin 20(l113.7 2,884,503 4/59 Connelly 200-172 2,975,258 3/61 Higginbottom. 2,984,726 5/61 Roeser. 2,999,142 9/61 Woodhall et al. ZOO-413.7 X

BROUGHTON G. DURHAM, Primary Examiner. 

1. A UNITARY CONTROL ASSEMBLY FOR TRIP-FREE USE ON MANUAL RESET THERMOSTATIC ELECTRICAL SWITCHES COMPRISING: A HOUSING HAVING MEANS FOR ATTACHMENT TO SUCH A SWITCH, A GUIDE SLEEVE HAVING OUTER AND INNER END PORTIONS AND EXTENDING FROM SAID ATTACHMENT MEANS, SAID GUIDE SLEEVE HAVING AT LEAST ONE INSIDE AXIAL SLOT, A SWITCH-OPERATING RESENT PIN EXTENDING THROUGH SAID SLEEVE, ONE END OF SAID RESET PIN HAVING AN AXIALLY DIRECTED SWITCH-OPERATING MEANS AND AT LEAST ONE TRANSVERSE LUG FOR PASSAGE THROUGH SAID SLOT WHEN THE PIN IN INSERTED THROUGH SAID SLEEVE, A TRANSVERSELY DIRECTED RETURN SPRING EXTENDING ACROSS THE INNER END PORTION OF THE SLEEVE AND ENGAGED BY SAID SWITCH-OPERATING MEANS, AT LEAST ONE EAR ON THE SPRING EXTENDING TOWARD THE INNER END OF SAID SLOT FOR ENGAGEMENT BY SAID LUG UPON INSERTION OF THE PIN THROUGH THE SLEEVE THEREBY SUBSTANTIALLY TO DEFLECT THE SPRING TO ADMIT THE LUG FOR LOCATION UNDER THE SLEEVE, SAID EAR UPON ROTATION OF THE PIN PREVENTING REALIGNMENT OF THE LUG WITH THE SLOT WHEN THE SPRING RETURNS AFTER SAID SUBSTANTIAL DEFLECTION, SAID SPRING BEING ARRANGED TO PUSH BACK THE PIN UNTIL THE LUG ENGAGES THE INNER END PORTION OF SAID SLEEVE WHEN THE LUG IS UNALIGNED WITH THE SLOT, WHEREBY THE PIN IS HELD AGAINST SEPARATION FROM THE SLEEVE AND SAID SWITCH-OPERATING MEANS IS LOCATED TO ACCOMMODATE SWITCH-OPENING ACTION OF THE THERMOSTATIC SWITCH, A MANUAL CONTROL MEMBER ADJUSTABLY CONNECTED TO THE OUTER END OF THE RESET PIN FOR ENGAGEMENT WITH THE OUTER END PORTION OF SAID SLEEVE, THE ADJUSTED POSITION OF THE CONTROL MEMBER ON THE PIN BEING SUCH AS TO LIMIT PIN MOVEMENT BY SAID ENGAGEMENT TO PROVIDE FOR TRIP-FREE SWITCH OPERATION BY SAID CONTROL MEMBER OF THE THERMOSTATIC SWITCH. 